The present invention relates to the reaction of hydrogen gas with body centered cubic phase alloys, and particularly to the rapid reaction at mild temperatures of hydrogen gas with solid solution alloys having a body centered cubic phase structure.
Most metals that form hydrides react very slowly in bulk form at room temperature with hydrogen gas. Metallic niobium and metallic vanadium, for example, are relatively inert in bulk form at room temperature in the presence of hydrogen gas, with the hydrogen only slowly reacting with the body centered phase structure of each metal to form a precipitated niobium hydride or vanadium hydride. In the case of niobium, for example, attempts to increase the rate of reaction by plating the niobium with nickel or palladium or iron have been reported.
Metallic titanium is also relatively inert in the bulk form at room temperature in the presence of hydrogen gas. With titanium, the hydrogen only slowly reacts with the hexagonal close packed phase structure of titanium to form a precipitated titanium hydride.
In addition to the metals which form hydrides, a variety of alloys and intermetallic compounds which react with hydrogen are known in the art. U.S. Pat. No. 4,075,312 (Tanaka et al.) discloses titanium alloy hydride compositions containing at least one metal selected from the group consisting of vanadium, chromium, manganese, molybdenum, iron, cobalt, and nickel. J. J. Reilly et al., Inorganic Chemistry, 1974, Vol. 13, page 218, disclose intermetallic compounds of iron and titanium, FeTi and Fe.sub.2 Ti, which form iron titanium hydrides. J. F. Lynch et al., Advances in Chemistry, 1978, Vol. 167, pp. 342-365, disclose titanium-molybdenum alloys useful for hydrogen isotope separation. U.S. Pat. No. 4,228,145 (Gamo et al.) discloses a Laves phase intermetallic compound, TiMn2, which forms hydrides.
For many applications of metal hydrides, such as hydrogen storage, it is desirable to form the hydride from bulk metal or alloy, pulverize the hydride into some of granular or powdered structure, and thereafter cyclically remove hydrogen to form a lower hydride or the free metal or alloy, and thereafter reintroduce hydrogen to form the hydride. Starting with the bulk metals or bulk alloys described heretofor, it is necessary to go through an induction period, wherein the metal is heated to a high temperature such as 300.degree. C.-700.degree. C., then reacted with hydrogen at high pressure and then cooled very slowly until a temperature below about 100.degree. C. is reached (preferably about room temperature). At the high temperature, the rate of hydrogen dissolving in the metal is increased so as to achieve saturation in a matter of minutes rather than hours or days. At the high temperature, however, the equilibrium hydrogen pressure is so high that relatively little hydrogen actually dissolves to form hydrides. Accordingly, it is only upon a gradual cooling that sufficient hydride is formed. While many metals require only a single induction process to form the hydride, with the subsequent hydride powder cycling at a reasonable reaction rate, it should be apparent that the induction process represents a distinct disadvantage in forming and utilizing metal hydrides.
Recently, it has been discovered that certain body centered cubic solid solution alloys react rapidly with hydrogen at mild temperatures. More particularly, U.S. Pat. Nos. 4,425,318 (Maeland et al.) and 4,440,737 (Libowitz et al.) disclose body centered cubic solid solution alloys of niobium, vanadium, and tantalum (among others) which react rapidly with hydrogen under mild conditions. In addition, U.S. Pat. No. 4,440,736 (Maeland et al.) discloses titanium based alloys which react rapidly with hydrogen under mild conditions in which the body centered cubic structure has been stabilized by the addition of a body centered cubic metal such as vanadium, niobium or molybdenum.